The present invention relates to an apparatus for producing compost from manure by means of fermentation, in which an oxygen-containing gas and also a gaseous and/or vaporous phase originating from the manure is passed through the manure. Such a procedure is known. In it micro-organisms contained in the manure produce, inter alia, ammonia, part of which is converted directly into nitrates and part is entrained with the said phase from the manure. As a result of passing said phase through the manure, a part of the entrained ammonia is again converted into nitrates in the manure, with the result that this part of the ammonia is also advantageously used.
As a result of the processes occurring in the manure, the temperature of the latter gradually increases. For the fermentation process to proceed correctly, the temperature must, however, be kept within certain limits. For this purpose, an oxygen-containing gas such as air is supplied in a known manner to the manure in order to cool the latter and keep it within a required temperature range. As a consequence of supplying this additional volume of air, in order to avoid pressure build up, a corresponding volume of the gaseous and/or vaporous phase has to be discharged into the atmosphere. This means that a part of the ammonia contained therein is lost and can therefore not be advantageously used for the production of nitrates, as a result of which the quality of the compost obtained is lower than if all the ammonia were converted into nitrates. A further disadvantage is that this part of the ammonia is returned to the environment.